The true cause of this problem still remains a topic of debate. Early on there was a theory that hypermobility of the joint at the base of the big toe was the problem. Hypermobility refers to increased motion or movement in a joint.

But studies have not been able to show this is true. The next theory tested was that decreased ankle motion and flat feet contributed to the development of bunions. This hasn't been proven either.

Scientists have X-rayed and measured bone and joint angles looking for an anatomical explanation. Others have looked for imbalances in the surrounding soft tissues such as the muscles, tendons, and ligaments as a possible cause of the problem.

It's likely there are multiple factors for each patient with this deformity. There may be a genetic component. Shoe wear may add to the speed at which the deformity progresses and the degree or severity of deformity. More study is needed to answer the question more fully.